vim, duplicate whole line to the end of each line?

How to copy the current line content to the end of each line for the whole file ? For example:

From

hello 
world 
!

To

hello     hello 
world     world 
!         !

:%s/^\(.*\)$/\1 \1

• % - whole file
• s/^\(.*\)$ - match line from the beginning to end
• /\1 \1 - replace it with matched text two times.

There may be a problem with formatting those lines in columns. Here is an example:

hello           hello
hello           hello
world           world
!           !

This can be solved with addition of trailing spaces, the the shorter lines, like this: (. - denotes trailing space)

hello           hello
hello           hello
world           world
!....           !....    

As mentioned by @mattb in the comment, column formatting issue can be fixed with column command (it has to be on your PATH though): :%s/^\(.*\)$/\1 \1/ | %!column -t